Electronic oscillators for generating periodic or oscillating signals are fundamental to many radar, communication and clock systems. These circuits may take on many different configurations, including those which utilize MEMS resonators, such as surface acoustic wave (SAW) resonators, to produce a single frequency oscillating signal. For electronic oscillators, including those utilizing MEMS resonators, phase noise is a significant limiting factor in system performance. For example, an ideal oscillator generates a pure sine wave with all signal power occurring at a single frequency. However, in practice, the output signals of oscillators include phase modulated noise components that spread signal power to adjacent frequencies and result in noise sidebands.
Electronic oscillators may utilize various cancellation schemes in an effort to reduce these phase errors. For example, a conventional noise cancellation technique may include the use of a voltage controlled radio frequency (RF) phase shifting circuit responsive to the output of a resonator, as well as to a phase error feedback signal, for generating a phase-corrected output signal. However, the phase noise floor of the oscillator as a whole is a function of, and thus limited by, insertion losses associated with these phase shifting circuits. This is due to the thermal noise floor limiting the absolute floor at room temperature to nominally −174 dBm/Hz which is defined by K T B, where K is Boltzmann's constant in Joules/° K (Kelvin), T is temperature in ° K, and B is the overall bandwidth in Hz. This is referred to as “thermal noise” because of the dependency on temperature. Reducing the loop insertion loss allows for an increase in signal to noise ratio limited only by the power internal to the oscillator loop.
Alternative systems and methods for providing low phase noise in electronic oscillators utilizing MEMs resonators are desired.